The present invention pertains to brushless servo motors, and more particularly, to the construction and alignment of such a motor to define a repeatable angular relationship between signals from a motor position sensor and the relative angular position of a rotor shaft with respect to a motor housing.
Every brushless servo motor is equipped with a position sensor which provides signals representative of the actual instantaneous angular position of a permanent magnet rotor. These signals are used in a servo amplifier as a part of a servo system internal position loop for controlling the phase of currents to a plurality of stator windings in a proper sequence to cause the motor to operate. The position sensor and servo amplifier provide electronic commutation of the brushless servo motor windings. The integral position sensor, for commutation purposes, must be absolute at least within one electrical revolution of the motor. However, if this sensor can provide an absolute position feedback throughout the entire mechanical revolution of the motor, it can be used for the external position feedback loop which is closed around the entire servo system.
Prior art brushless servo motors require an initial adjustment and calibration of the position servo loop. This adjustment is different for each individual servo system/load combination because there is no specific angular relationship between the servo motor shaft, the mounting surface of the motor and the position sensor output signals. If a motor needs to be replaced, the new motor must be put in place and the position servo loop must be readjusted in order to provide a proper alignment between the load and servo motor position feedback signals.